Checking for the doublebuffer flag can cause confusion if no VBO has
been allocated for the buffer. Checking for allocatedMemory is the
more direct approach.

This fixes a regression in EverQuest 2.

wined3d: Use shader_sm1_read_dst_param() and shader_sm1_read_src_param() in shader_get_registers_used().

This reverts commit 8044c11e.